Warm the stock in a saucepan over medium heat. Add the wine to it and set aside.
Add the pancetta to a large sauté pan over low-medium heat. Let it cook for about 5 minutes, stirring occasionally. This will add flavor and grease the pan a bit.
Add 1 tablespoon of the butter and the onion to the pan and stir to combine. Cook the onion until it's soft, about 5 minutes.
Stir in the thyme and rice and mix to coat all of the rice grains with the butter and fat from the pancetta.
Add about 1 cup of the hot stock/wine mixture, just enough to cover the rice.
Letting it simmer, with near-constant stirring, add the stock/wine mixture as needed, about 1 cup at a time to cover the rice. The rice will slowly absorb the liquid, becoming creamy.
After about half of the liquid is added, add the chard and continue stirring and adding the liquid until the rice is al dente (the very center of each grain of rice will still have a bite to it). You should still be able to see some of the liquid as this is a "loose" rice dish -- when you serve it, it will fall a bit.
Add the lemon zest and juice, the remaining 2 tablespoons of butter and the Parmesan. Season generously to taste with salt and pepper.
Serve immediately.